Microbiologists have tested planes and found that germs are commonplace, and can survive for hours or days after the passenger who brought them on board has departed, with viruses like MRSA and E. coli living on the plane for over a week.

As well as causing the common cold and influenza, these bugs and viruses can cause everything from skin diseases and upset stomachs.

Some research suggests that low humidity interrupts the Mucociliary Clearance System, which consists of a thin layer of mucus and tiny hairs in the nose that usually traps viruses and bacteria and moves them from the nose to the throat, where they are swallowed and destroyed by acid in the stomach.

Because this system no longer works properly, bacteria and viruses get easier access to your lungs.

Add to this the fact that you are planes are often filled with people from many different countries carrying strains of virus that your body hasn’t come into contact with before, and it’s not wonder that you are more likely to get sick.

The low relative humidity of cabin air means that bacteria and viruses get easier access to your lungs

So how do you stay healthy on a flight?

The number one rule is to not touch your eyes, mouth or the inside of your nose, although that can be very hard to do.

A more realistic option is to make sure your hands are clean if you do touch your eyes, mouth or nose, by washing them well with soap and water, and frequently applying a hand sanitiser gel containing at least 60 per cent alcohol.

Remember to do this before a meal and as soon as you can after your flight.

It’s a good idea to wipe down as many surfaces as you can with the gel or antibacterial wipes too, such as the remote control, tray table, video monitor screen and other surfaces known to have high levels of bacteria.

Similarly, try not to touch places that are accessible to a lot of people, like the top edges of aisle seats, door handles, or bathroom mechanisms.

A moisturising nasal spray will also help combat that low humidity by helping the Mucociliary Clearance System do its work.